An official website of the United States government.

Due to a lapse in appropriations, EPA websites will not be regularly updated. In the event of an environmental emergency imminently threatening the safety of human life or where necessary to protect certain property, the EPA website will be updated with appropriate information. Please note that all information on the EPA website may not be up to date, and transactions and inquiries submitted to the EPA website may not be processed or responded to until appropriations are enacted.

We've made some changes to EPA.gov. If the information you are looking for is not here, you may be able to find it on the EPA Web Archive or the January 19, 2017 Web Snapshot.

Aquatic Life Criteria - Ammonia

EPA has published final national recommended water quality criteria for the protection of aquatic life from the toxic effects of ammonia in freshwater. EPA's 2013 ammonia criteria reflect new data on sensitive freshwater mussels and snails, incorporate scientific views EPA received on its draft 2009 criteria, and supercede EPA's previously recommended 1999 ammonia criteria. In addition to the criteria document, EPA has also published supporting information to assist states, territories, and authorized tribes considering adoption of the new recommended criteria into their water quality standards.  In 2018, EPA corrected a minor typesetting error in the EPA Aquatic Life Ambient Water Quality Criteria for Ammonia (2013) document, EPA corrected the error and has republished the document below.  The equation to calculate the ammonia criterion maximum concentration (CMC) where Oncorhynchus species are absent was missing parentheses which are needed to correctly calculate the criterion (p 42). The error did not affect the results for the criterion values presented in Figure 5a (p 43) and Table 5b (p 45), and the equation is correct in Appendix N: Site-Specific Criteria for Ammonia (p 227).

If you have questions please contact Christine Bergeron at Bergeron.Christine@epa.gov.

On this page:

What is Ammonia?

Ammonia is one of several forms of nitrogen that exist in aquatic environments. Unlike other forms of nitrogen, which can cause nutrient over-enrichment of a water body at elevated concentrations and indirect effects on aquatic life, ammonia causes direct toxic effects on aquatic life.

Where does Ammonia Come From?

Ammonia is produced for commercial fertilizers and other industrial applications. Natural sources of ammonia include the decomposition or breakdown of organic waste matter, gas exchange with the atmosphere, forest fires, animal and human waste, and nitrogen fixation processes.

Ammonia can enter the aquatic environment via direct means such as municipal effluent discharges and the excretion of nitrogenous wastes from animals, and indirect means such as nitrogen fixation, air deposition, and runoff from agricultural lands.

How does Ammonia affect Aquatic Life?

When ammonia is present in water at high enough levels, it is difficult for aquatic organisms to sufficiently excrete the toxicant, leading to toxic buildup in internal tissues and blood, and potentially death. Environmental factors, such as pH and temperature, can affect ammonia toxicity to aquatic animals.

You may need a PDF reader to view some of the files on this page. See EPA’s About PDF page to learn more.